1. Field of the Invention
This invention relates to a method for improving storage stability of an anaerobically hardenable thermosetting resin. More particularly, it relates to a method for improving storage stability of an anaerobically hardenable thermosetting resin (hereinafter referred to as epoxy ester resin) dissolving a reaction product of an epoxy resin with and .alpha.,.beta.-unsaturated monocarboxylic acid (the reaction product will be hereinafter referred to as epoxy ester) into a polymerizable olefinic unsaturated compound (hereinafter referred to as an unsaturated monomer) and also an anaerobically hardenable thermosetting resin composition with improved storage stability. The term "anaerobically hardenable thermosetting resin" herein used is intended to imply that which is chemically stable for a long period of time in the presence of a molecular oxygen containing gas such as air but which is considerably lowered in storage stability and tends to gel within a short period of time in the absence of molecular oxygen.
2. Prior Art
In recent years, a number of thermosetting resins have been practically applied in various fields due to development of significantly advanced techniques therefore. Of many thermosetting resins, unsaturated polyester resins are rapidly increasing in demand because of their excellency in property and wide aplicability. In particular, unsaturated polyesters reinforced with glass fibres (hereinafter referred to as FRP) are now in wide use in the field of composite material. However, as the range of use of the FRP resin is increasing, there is induced a strong demand of high quality FRP resins having excellent properties such as high elongation, high physical strength, excellent resistances to corrosion and heat, etc., which can hardly be satisfied with the unsaturated polyester resins. Under these circumstances, epoxy ester resins have been studied and developed in order to satisfy the above-mentioned demand. Especially in the field where corrosion resistance is required, application of the epoxy ester resins has been intensively studied, leading now to practical application as tanks, pipes, ducts, etc. However, the epoxy ester resins have some disadvantages, one of which is that they are very susceptible to anaerobic hardening. This undesirability places a limit on application of the resins. In general, the epoxy ester resins which have been once prepared are irresistibly placed in hermetically sealed vessels such as cans, drums, containers, tanks, etc., for purposes of transportation or storage. However, the resin is unstable in the hermetically sealed state because of its tendency to anaerobic hardening and thus tends to gel during the storage or transportation, presenting a serious problem on practical application. Undesirably the anaerobic tendency is not reduced at all even if known stabilizers for thermosetting resin such as, for example, quinones, hydroquinones, nitro compounds and the like, are used in an increased amount. In order to prevent the resin from gelling during transportation or storage, it is general to cause the resin in a vessel to contact with air by taking off the seal, and agitating or shaking the vessel at regular intervals. However, this method requires much time and labor and will be rather troublesome, resulting gellation in some cases.